Servo - January 2008

REVIVING A SHOWBOT

and the left motor would respond to forward and back on the joystick.

Although ARTI can’t rotate in place with this steering setup, he is easy to control.

No matter how the trim tabs on the transmitter were adjusted, there wasn’t enough range of travel to center the signal. To fix it, the radio was going to need some work. (I always seem to find a reason to take things apart!)

After pulling the back off the transmitter, I saw that there was an extra hidden adjustment on each trim tab (see the photo). These must have been used by the factory to help center the signal for their system. By adjusting these, I was then able to set the correct center via the trim tabs on the front of the radio.

Once this was done, the drive motors were off with the right stick centered and the steering responded well at each edge. That took care of the motion part. Now we just need to figure out what the other channels control and how they work.

Extra (hidden) trim adjustment.

Charging transformer.

What Else Can ARTI Do?

Since the robot started making that siren sound when first powered up, I knew that moving the left joystick side to side turned on the siren. It did that without having to move the stick too far, but it did nothing when moving it in the other direction. I thought it might do something more, so again I had to adjust the extra trim tab inside the radio to help center the signal. This moved the center of the signal and all of a sudden, the robot would make another different warbling siren sound with the stick in the other direction. It also required the stick be moved a bit more to enable the original siren sound, so that it wouldn’t be turned on by mistake. Things were definitely starting to shape up!

The last channel is controlled by the up and down movement of the left joystick and would turn on/off the onboard tape player. This one didn’t need much adjustment and since the left stick is normally for a throttle, it

has a detent to stay in place. This was perfect since you could turn on the tape deck and wouldn’t have to hold the stick to keep it going.

When the robot was reassembled and the body screwed back on, I turned on ARTI and absolutely nothing happened. If I tapped on the circuit breaker, he would power on for a second or two. Since it seemed like it was bad, I picked up a replacement at the local electronics shop (Abel Electronics.) The body was pulled back off the robot and then the circuit breaker was replaced.

ARTI was turned on again but nothing happened. Upon closer inspection, I found there was a bad connection where the terminal was crimped on the wire going to the breaker. The wires had been tinned and then crimped to the terminals. The crimped connection loosened up a bit and, as a result, oxidized between the connector and the wire which caused an intermittent connection at that spot.

It would have been better if the connector had just been crimped to the wire itself (without tinning it first) or soldered after crimping. I’ve heard arguments both for and against soldering crimped terminals so just use

what works best for you whenever encountering a similar problem. Replacing that connector and reassembling the robot took care of the last issue with the robot itself.

Whenever the robot is powered on, the eyes will light up in a blue color and the mouth lights up red. If the tape player is enabled or the operator is speaking, the light for the mouth will flash in time with whatever sound ARTI is making. This is a great visual aid when the robot is speaking. Kids have found it very appealing when we play a book on tape.

The remaining gadget to tackle was the wireless communicator used for the operator. The unit on the robot was made by OHRA and would both receive and transmit sound. The one in the robot was customized a bit to integrate it into the robot. I would either have to find the correct match for it or replace the whole thing to get that portion to work. It was just a stroke of good luck that one of the few (very few) links that turned up was for a set of OHRA Walkphone full duplex communicator (OR-200) units still in the original boxes.